Windblown snow, sand, and dust can create hazardous driving conditions by reducing visibility and forming drifts on the roadway that block or impede traffic movement. Blowing snow also causes icy roads, which are a major cause of vehicle accidents. Blowing snow also causes significant problems on railroads by forming drifts that block the passage of trains where tracks pass through cuts in hills, and by clogging switches and interfering with the operation of electronic sensors for detecting over-heated journals and dragging equipment.
To alleviate the problems created by blowing and drifting snow, snow control devices in the form of snow fences and other structures have been used for more than 100 years. A snow fence causes the wind-borne snow crystals or particles to settle out of the wind in a protected or sheltered area other than at the critical area of the roadway or railroad tracks where snow accumulation is not wanted. The typical construction of a snow fence is a two-dimensional panel with a series of slots, holes or openings formed through the panel to create porosity. The snow fence creates aerodynamic drag and alters the structure of the turbulence which slows the velocity of the wind and diminishes its capacity to carry snow. In addition, a porous snow fence reduces the scale of turbulence by breaking up large eddies into smaller ones. These effects on the airflow allow the suspended particles to settle out and accumulate in an area which is protected or sheltered by the snow fence. In the case of a porous fence, most of this deposition occurs on the downwind side of the barrier or panel. By positioning the snow fence far enough away from the roadway, the snow settles out of the wind at the sheltered or protected area. The wind is relatively free of snow close to the protected area so no further snow accumulates at the critical area of the roadway. However, because the wind will pick up additional snow particles by blowing over expanses of snow-covered ground, the snow fence and its protected area must be close enough to the roadway or other critical area to prevent the wind from accumulating snow again before reaching the roadway or critical area. Otherwise, the placement of the snow fence will be ineffective in preventing snow accumulation on the roadway or critical area.
Typically, the panels of a snow fence are assembled in long continuous rows, which are visually obtrusive and aesthetically objectionable in a natural environment. The panels should be situated generally perpendicular to the prevailing wind direction to achieve the maximum effectiveness. The effectiveness of a two-dimensional fence decreases as the angle between the wind direction and the fence alignment decreases below approximately 60 degrees. The holes or slots are sometimes prone to clogging with snow, which reduces the effectiveness of the snow fence. The panels are typically constructed of wood, steel or plastic sheeting and the panels are attached to the ground by posts or by triangular support frame structures to hold up the panels. Conventional snow fences require time-consuming field fabrication and installation, and are often prohibitively expensive. Their use is often restricted by the need to place the fences outside of the existing right-of-way and the reluctance of landowners to grant the necessary easements. Because of the difficulty and cost of assembling these types of snow fences, they are generally not removed during those seasons of the year when they are not needed. Consequently, the snow fences create an obtrusive unnatural environmental impact on a year-round basis. Furthermore, an errant vehicle that accidentally departs the roadway and collides with one of these snow fences may incur serious damage and possibly injure the occupants as a result of the bulk and rigidity of materials used to construct the snow fences.
Natural vegetation such as trees and brush are sometimes planted adjacent to roadways and railroads and at other locations to create natural windblown particle control obstacles. While often effective when mature, the natural vegetation remains ineffective until it has grown to a size capable of interacting with the wind. The time to achieve this growth may be significant, particularly where growing conditions are suboptimum. Moreover, not all of the planted vegetation survives and attains a size sufficient to control windblown particles. It is not practical to move or adjust the positioning of the natural vegetation after it has been planted to obtain the best control benefits. The soil types and weather conditions in some locations preclude the use of natural vegetation for controlling windblown particles. Consequently, man-made artificial structures are often preferred for use to control windblown snow because they can be placed where needed and are immediately effective. It is theoretically possible to remove the artificial structures during the seasons of the year when they are not needed, although the reality is that these artificial structures are rarely if ever removed once constructed because of the cost and inconvenience of doing so.
Because of the cost, obtrusiveness and removal difficulties associated with most of these artificial snow fences and particle-control structures, they are not prevalently used for other beneficial purposes such as accumulating snow in agricultural fields to increase the soil moisture content for growing crops, retaining the topsoil against wind erosion, or shielding immature plants from the shear stress of wind and rapid evaporation of soil moisture at their critical early-growth stages. These and other beneficial uses of windblown particle control devices would become more prevalent if the cost of the control devices were reduced so that more of them could be used to create beneficial effects throughout large expanses of the agricultural fields, if the ability to assemble and disassemble the devices was enhanced so that the devices could be removed after stable plant growth had been established and to permit harvesting of the crops, and if the cost-benefit considerations of using such devices were more pronounced, among other things.
In addition to controlling windblown particles, various silt and sediment control devices and artificial reef structures have been devised to deposit and control silt, sediment and other water-borne particles in moving bodies of water. In general, however, the fluid dynamic drag and turbulence effects necessary to control water-borne particles are much different than the effects necessary to control windblown particles. For example, the fluid dynamic effects are related to the density of the medium in relation to the density of the transported particles, and the square or cube of the flow velocity. The density of water is approximately 1000 times that of air and the velocity of snow-transporting wind is typically 10 times the speed of sediment-transporting water. These considerations indicate magnitudes of difference in the fluid dynamic effects, thereby suggesting that the structures which are effective in controlling water-borne silt are essentially ineffective and inapplicable to controlling windblown particles.